1. Field of the Invention
This invention relates to telecommunications systems, especially PBX/Server systems, also referred to as Multi-Line Telephone Systems (MLTS). Specifically, the invention relates to completing an emergency, e.g. 911, call from a station/device and delivering precise location information of the caller when the emergency caller disconnects immediately.
2. Brief Description of the Prior Art
When a caller calls an emergency number, e.g. 911, the call is routed to a Public Safety Answering Point (PSAP). In some jurisdictions, regulatory agencies require that the caller's telephone number/callback number and/or precise physical location referred to as an Emergency Location Identification Number (ELIN), be automatically provided to the PSAP. This information is used to locate the caller and to call back to the caller should there be a disconnect.
A caller identification (i.e., telephone number and ELIN) may be delivered to the PSAP either in-band (e.g., using DTMF signaling) or out-of-band (e.g., using ISDN signaling) depending on the type of trunk circuit employed. For residential callers Caller ID number is sufficient for the PSAP. For PBX/server service many users, e.g., commercial callers, hotel guests; an ELIN is required for this complex environment, for example, street address, floor number, room number, desk number. In some cases, the ELIN is geodetic, i.e. includes earth coordinates or GPS data.
Modern PBX/MLTS systems provide many new features to accommodate the way modern businesses operate. For example, employees may be assigned personal identification numbers (PINs) that are used by the PBX/MLTS to identify the employee and assign a telephone number to him/her. Further, for example, if an employee is assigned to a different location in the building, an automatic relocation feature can be activated using the PIN to reassign the employee's telephone number to the new location.
Another feature of PBX/MLTS systems is that some telephones connected to the PBX/MLTS system may not be provided with the ability to receive direct (inward) dialed calls. For example, in a hotel, telephones in rooms are typically not capable of receiving a direct inward call from outside the hotel, therefore they have no known Caller ID to identify them to the PSAP.
Still another feature of modern PBX/MLTS systems is that it is possible to make many or even all telephone lines available for use by multiline devices connected to the system. Thus, a caller from behind the PBX/MLTS system may be identified by many different telephone numbers.
All of these features of modern PBX/MLTS systems present problems for transmitting call back number and ELIN to a PSAP in an emergency call. In many situations, the only callback number provided from the PBX/MLTS system is the main directory billing number. In situations where the caller has utilized the automatic relocation feature of the PBX/MLTS system, the caller will be identified by employee PIN but not by a specific location. In situations where the caller has no direct inward call receive capability, the PSAP cannot call back the caller in the event of a disconnect. In the situation of a call from a multiline device, the telephone number from which the emergency call is made may not be the primary number for the caller and a return call to that number may cause a different device to ring rather than the caller's device. Moreover, the number used by the emergency caller may be associated with a ELIN which is not the caller's ELIN.
Co-owned co-pending application Ser. No. 09/816,830 and co-owned co-pending application Ser. No. 09/816,843 discloses method and apparatus for accurately reporting the ELIN of an emergency caller behind a PBX/MLTS system to a PSAP.
The methods include assigning a port equipment number (PEN) to each device/trunk associated with the PBX/MLTS system, maintaining a database of ELIN and callback numbers associated with PENS, identifying an emergency number when it is dialed, invoking an emergency service routing upon detection of a dialed emergency number, associating the PEN with the dialer of the emergency number, retrieving the ELIN and callback number from the database, and transmitting the ELIN and callback number to the PSAP. The apparatus includes database management means, emergency number detection means, call routing means, ISDN and non-ISDN signaling means. The apparatus may be configured so that either the callback number, the ELIN, or both are transmitted to the PSAP. Further, the apparatus may be configured to recognize multiple emergency numbers and to give emergency calls priority over non-emergency calls.
The specificity of the ELIN can be determined by the system administrator and additional text information may be associated with the ELIN. The call routing and signaling means are capable of routing the emergency call through multiple PBX/MLTS systems before reaching the public network.
One problem that is not solved by the co-owned co-pending applications is the problem of a caller immediately disconnecting an emergency call before the ELIN/callback number can be transmitted to the PSAP. Such a situation might occur in different ways, e.g. criminal activity forcing unintentional hang-up, accidental dialing followed by intentional hang-up, an emergency requiring immediate flight, etc. The PSAP may receive the primary billing number but not the accurate ELIN/callback number. This results in ambiguity for the PSAP. It may be impossible to determine whether the call was a mistake or whether and where the emergency is.